This invention relates to a power tool which may be used in and around environments which may be exposed to flammable substances while providing a configuration which is conducive for the operator to handle while transmitting high torque to the application.
Historically, power tools have been made to be lightweight yet provide a high level of power yielding a high power density. This was achieved by utilizing a type of motor called a universal motor.
A universal motor requires carbon brushes to transmit and commutate electricity to the rotating armature. The universal motor typically employs an air moving fan to move air through the motor housing to exhaust the heat from the motor. These motors typically operate at mains voltage supplies from roughly 10V AC to 240V AC.
Typically, power tools of this type use a snap acting contactor line switch to make and break the supply of the electric power supply.
This construction will allow any potentially explosive gasses to become ignited as the cooling fan causes them to flow through the tool and come in contact with either the electric arc at the brushes or the switch.
One such system is described in U.S. Pat. No. 2,155,082, the Decker patent where he describes a motor with brushes, a fan to produce airflow, air openings in the field case through which the air passes, a switch and gearcase.
Another type of power tool well known in the trade is the type powered by a battery. The motor typically utilized to power these tools is a permanent magnet motor. The permanent magnet motor operates from voltages of typically between 8V DC to 36V DC. The electric current is conducted from the battery through carbon brushes to the rotating armature. This so called “Cordless Power Tool” also employs a switch with contacts which cause an arc when the switch is operated. This type of tool offers the user the freedom of operation without a cord. However the tools are limited in their ability to transmit large amount of power for an extended period of time due to the finite amount of energy in the battery.
A typical universal motor and a typical permanent magnet motor produces a speed torque characteristic such that the torque is at a maximum when the speed is at zero rpm. This characteristic causes the motor and load to accelerate very quickly to full rpm. Typically this acceleration occurs in approximately 0.05 seconds.
Power tools may employ a brushless DC motor. This type of motor typically may produce a combination of speed and torque which produce a high power density similar to that of the previously mentioned motors. These motors do not employ carbon brushes and a rotating commutator to function thereby. Therefore, they do not produce any arc during operation. Yamamoto U.S. Pat. No. 7,053,567 discloses a brushless DC motor for use in a power tool. However this type of motor is controlled with a computer and an electronic switching circuit which characteristically produces a signature of electromagnetic interference (EMI).
Applications exist which demand a high torque and speed over an extended period of time. Some applications, for example aboard a Naval Aircraft Carrier, have such a requirement. These applications often require a large amount of power to complete the necessary work. The amount of power required is significantly greater than is practical to be stored in a portable battery attached to a tool.
These applications have the need to move a substantial mass in addition to the requirement for high torque and speed. Starting and stopping such a mass with a power driver such as a compressed air powered ratchet wrench, causes an adverse reaction to the operator. This reaction may result in a large force reaction which the operator must counteract.
Some such applications for high power requirements are subject to exposure to potentially dangerous fluids and gasses such as on an aircraft carrier or in an aircraft hanger. Additionally, these applications may be exposed to salt spray and rain. Additionally, the ambient temperature on board an aircraft carrier, for example may be very extreme ranging from a negative 40 degrees Celsius to a positive 60 degrees Celsius.
Many applications such as those mentioned have the additional requirement to be very mobile. Lui U.S. Pat. No. 7,109,613 discloses a power tool which is protected from liquids. The invention describes an enclosure which protects the motor from liquids with a thermally conductive part that is exposed to the exterior outside the body for the purpose of conducting heat from the motor for heat dissipation. Lui however is limited to dissipating heat to the outside through one end of the motor enclosure which is necessarily limited in surface area and consequentially may not conduct a large amount of heat at an ambient temperature of 60 degrees Celsius.
Vanjani U.S. Pat. No. 6,104,112 teaches of a sealed brushless DC motor with an integral controller. However Vanjani discloses the need for a heat sink, however, the invention provides a heat flow path for only the electronic controller and not the motor.
The Onsrud U.S. Pat. No. 2,862,120 discloses an efficient means of transferring heat from a sealed motor compartment to the exterior with a pair of eccentric shells separated by a series of variously dimensioned axially extending radial baffle ribs. The Onsrud patent however does not disclose the means for moving the cooling fluid past the cooling ribs.
Several applications, such as tasks to be performed on the deck of an aircraft carrier, require power to be transmitted quickly in environments which may become exposed to jet fuel or explosives from ammunition. These applications do not utilize mains power or compressed air due to the difficulty and hazard of dragging hoses or cable across the busy flight deck. Also it is not practical to use a gasoline powered compressor or generator as gasoline is not permitted on the flight deck due to the hazardous nature of gasoline. Diesel powered generators or compressors while permitted on a flight deck, are not practical due to the extreme weight which renders them not portable enough to rapidly deploy from application to application. Consequently, for many of these applications a manual hand powered crank tool, or speed wrench much like one manufactured by “Snap on Tools” Speeder, 18⅞″ Stock #S4 is employed. The use of this type of hand tool is extremely fatiguing for the operator and consequently the application is not completed as quickly as desired.
One such application is loading 20 mm artillery rounds into the magazine of a Gattling gun mounted in a jet fighter as one step in preparing the fighter to be redeployed. These rounds are entrained in a long chain which is stored in an ammunition storage car. The chain of ammunition stored is typically a quantity of 5000 to 6000 rounds. In addition to the rounds mass is the mass of the carrier chain which contributes to a substantial inertia. The ammunition is then transferred to the magazine inside the gun on the aircraft. A mechanism internal to the gun is a cranking mechanism which moves the chain of rounds into the gun and thereby fills the guns magazine with 500 to 550 rounds. This cranking mechanism requires approximately 20 to 25 foot pounds of torque to operate. The mechanism in the gun has a maximum torque capability which must not be exceeded or failure of the mechanism may result.
The operator must stand on a small elevated platform to allow him to be accessible to the gun cranking mechanism. The precarious position of the operator requires a smooth transfer of torque so as to not cause him to lose his balance and fall. A power tool such as described in the Godfrey U.S. Pat. No. 3,244,030 would provide a measure of control for management of the torque due to the positioning of the handle on an “L” shaped drill housing.
An additional application is to elevate the hinged wing sections of jet aircraft to allow more compact storage aboard aircraft carriers. Internal to the stationary portion of the aircraft wing is a crank mechanism which when rotated lifts the wing portion to the folded position. This typically requires a torque of between 20 to 25 foot pounds and requires approximately 300 revolutions to fully lift the wing. The wing elevation mechanism has a maximum torque capability which must not be exceeded or failure of the mechanism may result.
The application of cranking the wing up to the folded position and down to the deployed position requires both clockwise and counterclockwise rotation of the mechanism. A motorized means of raising and lowering the wing should have a means to assure the rotational direction of the motor does not change during operation. Cuneo U.S. Pat. No. 4,381,037 describes a means to prevent inadvertent motor reversal.
These two applications are now performed with a speed wrench. These operations require a team of up to five workers due to the intensity and fatigue of the operation.